The present invention relates to air intake manifolds for internal combustion engines, and in particular to an active intake manifold providing variable-length intake tracts between a throttle and an engine cylinder's intake port.
In past engine design practice, intake manifolds typically were designed with a fixed intake tract length (i.e., the length between an intake throttle and an engine cylinder's intake port) and intake tract shape, which were selected to optimize engine power output within a desired engine speed range. For example, at lower engine speeds, longer intake tracts are known to provide greater engine power output than obtained with shorter intake tracts, while shorter intake tracts are better suited to optimizing power output at high engine speeds. These differences are attributable to changes in the frequency and magnitude of intake back-pressure pulses generated by the opening and closing of the engine's intake valves at different engine speeds. As a result, designing an intake manifold typically involved compromise, because an intake manifold configuration selected to obtain optimum power output in one engine speed range would provide less-than-optimum power output in other engine speed ranges.
As internal combustion engine designs have advanced, designers have sought to minimize the inherent compromises in fixed-length intake manifold designs in order to increase available engine power output over a broader range of engine speeds. One approach has been to provide an intake manifold with two sets of intake tracts of different length feeding air to the engine cylinders' intake ports, along with a means of switching intake air flow between the sets of intake tracts when in different engine speed ranges. For example, a manifold may be provided with a set of short intake runners and a set of long intake runners, with the short intake runners blocked off by butterfly valves when at low engine speeds. When a predetermined engine speed (e.g., 4,000 rpm) is exceeded, the butterfly valves are opened to allow intake air to pass through the short intake runners into the cylinders to increase power output.
Implementation of a variable-runner manifold concept is not without its problems. In addition to accommodating multiple runner sets and runner actuators, variable runner manifolds must also meet a number of other design requirements, including providing mounting locations for appended devices such as exhaust gas recirculation (“EGR”) and positive crankcase ventilation (“PCV”) fittings, providing locations for fasteners to hold the manifold to the engine as well as access for installation or removal of the fasteners, accommodating irregular mounting flange shapes, being capable of being produced at reasonable cost, meeting acoustic requirements including government sound level limits, while providing driver-pleasing intake flow sounds. Compliance with the myriad design requirements represents a challenge to efficient packaging, production and installation of variable runner intake manifolds.
In view of the foregoing, it is an object of the present invention to provide an improved air intake manifold for an internal combustion engine. The present invention addresses the foregoing problems by providing a variable intake tract manifold which minimizes the space required for the intake tract-altering apparatus, thereby allowing designers greater freedom in arranging the manifold to accommodate the above design requirements, and provides these benefits with mechanically simple, reliable, easy to manufacture and cost efficient components.
In one embodiment of the present invention, there is provided an air intake manifold for an internal combustion engine with an air inlet port, two plenum chambers receiving air from the inlet port, a pair of long and short intake runners receiving air from the plenums for each engine cylinder and leading to a manifold outlet port, and a cylindrical rotary air flow control valve and valve actuator. One-half of the long runners draw air primarily from one plenum, with the remaining long runners drawing air primarily from the other plenum. The short runners draw air from both plenums. The cylindrical rotary valve controls air flow into the short runners and between the plenum chambers. The rotary valve is positioned over the inlet ends of the short runners and between the plenum chambers, such that as the rotary valve is rotated, it moves between a first position blocking air flow into the short runners and blocking air flow between the plenum chambers, a second position blocking air flow into the short runners and permitting the long runners to receive air from both plenum chambers, and a third position permitting all the runners to receive air flow from both plenum chambers.
The present invention thus provides a compact variable-tract intake manifold with at least three different intake tract configurations while significantly minimizing the space required by the variable-intake tract actuator, thereby allowing the intake manifold arrangements to be optimized to meet other design requirements while minimizing production costs.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.